Detection of mild to moderate influenza A/H7N9 infection by China’s national sentinel surveillance system for influenza-like illness: case series

British Medical Journal
13 July 2013 (Vol 347, Issue 7916)
http://www.bmj.com/content/347/7916

Research
Detection of mild to moderate influenza A/H7N9 infection by China’s national sentinel surveillance system for influenza-like illness: case series
Dennis KM Ip, clinical assistant professor1, Qiaohong Liao, public health officer 2, Peng Wu, post doctorate fellow1, Zhancheng Gao, professor and respiratory physician3, Bin Cao, professor and infectious disease physician4, Luzhao Feng, public health officer2, Xiaoling Xu, respiratory physician5, Hui Jiang, public health officer2, Ming Li, public health officer2, Jing Bao, respiratory physician3, Jiandong Zheng, public health officer2, Qian Zhang, public health officer2, Zhaorui Chang, public health officer2, Yu Li, public health officer2, Jianxing Yu, public health officer2, Fengfeng Liu, public health officer2, Michael Y Ni, clinical assistant professor1, Joseph T Wu, associate professor1, Benjamin J Cowling, associate professor1, Weizhong Yang, medical epidemiologist and deputy director6, Gabriel M Leung, professor1, Hongjie Yu, medical epidemiologist and director2
http://www.bmj.com/content/346/bmj.f3693

Abstract
Objective  To characterise the complete case series of influenza A/H7N9 infections as of 27 May 2013, detected by China’s national sentinel surveillance system for influenza-like illness.

Design  Case series.

Setting  Outpatient clinics and emergency departments of 554 sentinel hospitals across 31 provinces in mainland China.

Cases  Infected individuals were identified through cross-referencing people who had laboratory confirmed A/H7N9 infection with people detected by the sentinel surveillance system for influenza-like illness, where patients meeting the World Health Organization’s definition of influenza-like illness undergo weekly surveillance, and 10-15 nasopharyngeal swabs are collected each week from a subset of patients with influenza-like illness in each hospital for virological testing. We extracted relevant epidemiological data from public health investigations by the Centers for Disease Control and Prevention at the local, provincial, and national level; and clinical and laboratory data from chart review.

Main outcome measure  Epidemiological, clinical, and laboratory profiles of the case series.

Results  Of 130 people with laboratory confirmed A/H7N9 infection as of 27 May 2013, five (4%) were detected through the sentinel surveillance system for influenza-like illness. Mean age was 13 years (range 2-26), and none had any underlying medical conditions. Exposure history, geographical location, and timing of symptom onset of these five patients were otherwise similar to the general cohort of laboratory confirmed cases so far. Only two of the five patients needed hospitalisation, and all five had mild or moderate disease with an uneventful course of recovery.

Conclusion  Our findings support the existence of a “clinical iceberg” phenomenon in influenza A/H7N9 infections, and reinforce the need for vigilance to the diverse presentation that can be associated with A/H7N9 infection. At the public health level, indirect evidence suggests a substantial proportion of mild disease in A/H7N9 infections.